Electric load centers suffer from a number of limitations. Assembling the various components of the load center such as the trim panel to the metal enclosure of the load center oftentimes requires an electrician to align the holes in these components, insert screws through the aligned holes, and screw each screw into the holes. Such activities are time consuming and are oftentimes not successful on the first attempt and have to be repeated several times. In accordance with an aspect of the present invention, a push-in screw holder fixture for the metal enclosure is provided which enables an electrician to easily secure the trim to the metal enclosure.
There is sometimes created an overpressure condition within a load center which can cause the door of prior art load centers to be forced open. In accordance with an aspect of the present invention, a new and improved latch is provided which, during an overpressure condition within the load center, causes the latch to engage the latch receptacle on the trim panel even more securely so that the door does not open.
Because load centers are constructed in varying sizes, for each size of load center constructed by a manufacturer, a separate inventory of basepans had to be manufactured and maintained. A need has therefore developed for basepans which are adaptable to various sized load centers and which are relatively inexpensive to manufacture. This need was partially met by the production and use of extruded basepans. Alternatively, individual modular auxiliary basepan pieces were constructed for interconnection to accomplish circuit breaker load centers of adjustable length. Because angular mounting of components is not well suited to robotic assembly, some prior art basepans and modular extensions have had to be adapted to be vertically down loaded to mating portions of the basepan, or have been adapted to be horizontally or laterally connected to mating portions of the basepan. Such attachment methods and modular construction may not be desireable and can result in imprecise spacing between the connected modular pieces, which may affect the subsequent assembly and installation of components to the basepan and the basepan to the enclosure. In accordance with an aspect of the present invention, new and improved basepan and modular extension basepan components are provided which can be robotically assembled, but need not be robotically assembled in solely a vertical drop-down mode or a lateral mode, and which reduce the possibility of misalignment and improper spacing between connected modular pieces.
Securing the basepan to the enclosure is oftentimes time consuming and cumbersome. In accordance with an aspect of the present invention, an improved basepan is provided having mounting features which facilitate the assembly of the basepan to the enclosure, thus saving time and labor.
It is well known in the art to provide an electrically insulative barrier between the bus bars of load centers. In accordance with an aspect of the present invention, an improved basepan having integrally formed electrical insulative barrier is provided between the bus bars which increases the protection from the occurrence of arc tracking as well as decreasing the possibility of sustaining the arc, once it has occurred.
Bus bars have been secured to the basepan by common fastening devices such as screws, bolts and snap-in fasteners (U.S. Pat. No. 4,536,823) which can be cumbersome, time consuming to apply, uneconomical, require extra parts, and most importantly can impart stresses to the component being secured and adversely effect the structural integrity of the component. Applying ultrasonic energy to posts which are integral parts of a plastic basepan as a means of deforming the post to secure bus bars to the plastic basepan is well known (U.S. Pat. No. 4,118,754). Heat staking as a means of securing components to a plastic basepan can be advantageous in overcoming the above-stated disadvantages of common fastening devices, but imparts stresses which concentrate at the face of the basepan where the base of the post intersects the basepan to form corners. Such stress can significantly impair the integrity of the connection by causing a fracture of the post, loss of the integrity of the connection, and a decrease in the service life of the basepan and the load center. In accordance with an aspect of the present invention, an improved basepan is provided having integrally formed posts for securing thereto components such as bus bars and the like by heat staking which reduces the stresses imparted to the posts and basepans from heat staking.
As is well known, it has been difficult for installers to secure return wires to the neutral bars of the prior art load centers because it is generally difficult to see the holes in the neutral bar into which the wires are to be placed. In order to improve the visibility of the holes in the neutral bar into which the return wires of the power circuits are to be inserted and secured, and thereby facilitate the connection of the neutral return wires to the neutral bars by the electrical installer, in accordance with an aspect of the present invention an improved neutral bar is provided which allows for viewing of the electrical connector apertures positioned in the side walls when viewed either directly overhead or from the side.
Also, prior art attachment methods between the neutral bar and the basepan are unsatisfactory. In accordance with an aspect of the present invention, the neutral bar is adapted to permit simplified assembly and mounting to the basepan. This is accomplished by providing a configuration of the neutral bar and an improved basepan to which the neutral bar is attached which does not require the use of screws or other separate fastening devices thereby reducing the number of components in the load center and facilitating the mounting of the neutral bar to the basepan.
Furthermore, in order to further facilitate the installation of the return wires to the neutral bars of the load center, in accordance with an aspect of the present invention, an improved basepan is provided having an integrally formed neutral bar wire guide which assists the electrician or installer in guiding the wires of power distribution circuits into the electrical connector apertures in the neutral bars.
In accordance with another aspect of the present invention, an improved neutral tie bar is provided which connects the neutral bars together. Some load centers of the prior art are not grounded because the installer or user neglects to do so. There is nonetheless a need to assure that there is no potential difference between the neutral and the ground. In accordance with this aspect of the present invention, the neutral tie bar is adapted to be capable of being electrically connected to the outer metal enclosure of the load center thereby eliminating any potential difference between the neutral and ground of the load center. Since each power company providing service maintains the potential of the neutral at or close to zero volts, the function of connecting the neutral of the load center to the ground is accomplished by electrically connecting the neutral tie bar to the metal outer enclosure.
In accordance with an aspect of the present invention, a new and improved main lug insulator or barrier is provided between the incoming service and the other components in the load center functions to: insulate each of the main lugs from the neutral bus bar, neutral tie bar, and neutral lug(s); reduce incidental shorting or inadvertent energization of current carrying conductors both during installation and subsequent operation; and maintain required over-surface and through-air spacing for cooling and expansion of the main lugs.